1. Field of the Invention
The present invention relates to an electric actuator, i.e., an actuator to be operated by an electric motor, and more particularly, to position-detecting apparatus for detecting a rotated position of the output shaft of an actuator for opening and closing a damper of a vehicle air conditioner so as to make it possible to stop the motor at a predetermined position by pressing an appropriate switch so as to stop the damper at a selected position. The present invention also relates to a method for fixing brushes to the position-detecting apparatuses provided with various kinds of electric actuators.
2. Description of Related Art
When a plurality of brushes are provided, for example, on a movable portion of a position-detecting apparatus, brushes are individually heat-caulked onto the flat portion of a gear mounted on an output shaft. This method is described hereinbelow with reference to FIGS. 16 through 24.
As shown in FIGS. 16 through 19, a position-detecting apparatus (S) comprises a gear 30 and brushes 40 (40a and 40b). The gear 30 comprises an output shaft 32 and a disk 33 to which brushes 40 are fixed. The output shaft 32 and the disk 33 are integrated with each other through a boss 31. As shown in FIG. 18, the outer circumferential face 33a of the disk 33 contains gear teeth. Predetermined numbers of openings 34 are formed at predetermined positions of the disk 33. Supporting members 41 to be described later are inserted under pressure, or pressed into the openings 34 having a step 34a, respectively. The brushes 40a and 40b as shown in FIGS. 20 through 23 are fixed to the top surface of the disk 33 of the gear 30 by, for example, a heat-caulking.
The method for fixing the brushes 40 to the disk 33 is described hereinbelow taking the brush shaped as shown in FIG. 20 as an example. The supporting members 41 as shown in FIG. 22 are mounted on the brush 40a, and the supporting members 41 are fixed under pressure to the openings 34 formed at predetermined positions in the disk 33. The supporting members 41 are mounted on the flat portion 42 and the bent portion 43 of the brush 40a. The supporting member 41 comprises a portion 41a to be inserted under pressure into the opening 34 and a claw 41b which engages with a step 34a of the opening 34. Therefore, the supporting member 41 is prevented from being disengaged from the opening 34.
However, the position-detecting apparatus constructed by the above-described conventional method is required to be accurate in dimensions of respective brushes, in arranging the respective brushes at predetermined positions, and in the positions and dimensions of the openings formed on the disk to be used as a base body.
Further, when brushes are individually fixed to the flat portion of the disk of the gear by a heat-caulking, dimensions of projections formed on the supporting member to be heat-caulked and the dimensions of the brushes may differ from each other. As a result, the brushes are fixed to the flat portion of the disk of the gear at different angles, which causes the rotated position-detecting apparatus to detect the rotated position of the output shaft of the actuator with a low accuracy.
In addition, the fixing of the brushes to the disc one by one leads to the increase of the number of manufacturing processes.
As shown in FIG. 24, in the above-described position-detecting apparatus for detecting the position of the output shaft of the actuator for opening and closing an exhaust change-over damper, switching patterns 5a, 5b, 5c, 5d, and 5e connected to a switch for ventilation 4a, a switch for B/L 4b, a switch for heating 4c, a switch for heat/defrosting 4d, and a switch for defrosting 4e of an exhaust selection switch 4, respectively are concentrically formed on a printed body about a center axis. That is, the patterns 5a-5e, including their end edges, lie on different circumferences relative to that axis. A pair of brushes is mounted on one of both faces of a gear mounted on an output shaft in symmetrical relationship with respect to the output shaft. The slide terminals of the brushes slide on the switching patterns 5a through 5e, respectively.
In the above-described position-detecting apparatus, the position at which the actuator stops is affected in a great extent by the positions of the edges of the respective switching patterns, namely, by a manufacturing accuracy thereof. For example, if the edge position of a respective switching pattern is different from a predetermined value by "l", the angle error .theta. of the pattern edge, namely, the angle error which affects the stop angle of the actuator is expressed as follows: EQU .theta.=tan.sup.-1 l/R
where R is the radius of the pattern. That is, as the radius R of the pattern becomes small, the angle error of the pattern edge increases. Specifically, in FIG. 24, the usage of the pattern 5a allows the actuator to stop with a higher accuracy than the usage of the pattern 5b. Thus, when the pattern 5e nearest the center of a base body is operated, the actuator stops with the lowest accuracy. This is a great disadvantage of the conventional rotated position-detecting apparatus.